From The Discovery of Heredity:
[U]ntil the experiments of Francesco Redi and Jan Swammerdam in the mid-1660s, it was thought that insects and all other “bloodless animals” appeared from decay, rather than from mating between male and female. It took Redi’s careful experimentation, and Swammerdam’s observations, for them to come to the radical conclusion that “all animals come from an egg laid by a female of the same species.”
Huh. Just 350 years ago. Didn’t know that.
The question of the role of the male and the female in producing the offspring remained hugely contentious right up until the 1840s. Aristotle had argued that the male produced a “seed” (= “semen”), which the female nourished. Swammerdam, Steno and others turned this argument on its head and argued that the egg was the origin of all life – including in humans. Within a few years, matters became even more complicated when Antoni Leeuwenhoek observed spermatozoa in human semen. Leeuwenhoek thought that these sperm were the origin of life, and that the egg was simply food. Most people, however, argued they were parasitic worms (hence the name we still use today—“spermatoZOA,” or animal found in semen).
While the mechanics of what eventually became known as reproduction were finally worked out in the 1840s, in the middle of the 18th century people had begun to suspect that something else was going on.
Less than 170 years ago. Can you believe that?
“Lock up your daughters, lock up your wives….”
